Locally applied biomedical barriers and microbicides have proven ineffectual in preventing sexual transmission of HIV. We have recently found that HIV requires intact lipid rafts, highly specialized subregions in cell membranes, for entry into cells and for budding of fully infectious particles. Beta-cyclodextrin (beta-CD), a cyclic heptasaccharide that removes cholesterol from cell membranes and disperses lipid rafts, has been shown to block HIV infection and drastically reduce the infectivity of budding HIV particles. Cholesterol is also required by other pathogens some of which are associated with STDs. Beta-cyclodextrin is non-toxic and currently in human use as a carrier for polar drugs. Thus properly formulated, this molecule may be an effective microbicide with activity against HIV and other pathogens. Cholesterol has been shown to play a role in regulating sperm cell acrosomal reaction and depletion of sperm cell cholesterol by beta-CD induces capacitation and premature acrosomal reaction. The latter has been associated with low rates of fertilization. Thus beta-CD, by depleting sperm cell cholesterol, may prevent fertilization in vivo by inducing premature acrosomal reactions and reducing fusion efficiency. The central hypothesis of this proposal is that because it rapidly and efficiently depletes cholesterol from lipid membranes beta-CD has great potential as a combination microbicide-spermicide with low host cell toxicity. The goal of this project is to use in vitro and in vivo animal models to test the potential of beta-CD as a microbicide, particularly against HIV, and spermicide and to determine the mechanisms by which beta-CD inactivates H1V. The specific aims are: 1. To characterize and optimize the inhibitory effect of Beta-cyclodextrin on HIV-1 infection. 2. To determine the mechanisms by which Beta-cyclodextrin inactivates cell-free HIV-1 particles. 3. To determine the mechanisms by which Beta-cyclodextrin inactivates cell-associated HIV-1. 4. To determine the effects of Beta-cyclodextrin on sperm function in a rabbit contraception model. 5. To determine the effect of Beta-cyclodextrin in vitro on bacterial pathogens and vaginal flora. 6. To determine the anti-HIV microbicide potential of Beta-cyclodextrin in a Hu-PBL-SCID mouse vaginal challenge model. 7. To determine the microbicide potential of Beta-cyclodextrin against HSV, papillomavirus, and chlamydia trachomatis in animal models. This project takes advantage of the shared importance of cholesterol in the biology of sperm and HIV and other pathogens to develop a novel microbicide/contraceptive approach.